The present invention relates to systems and methods for the mapping of electronic, ionic, and electrochemical processes at a solid-liquid interface.
Understanding the local electrostatic, electrochemical, and double layer ion distribution at the solid-liquid interface is important in the study of corrosion, sensing, energy storage, and biological processes. These phenomena are governed by charge transport, diffusion, and electrostatic screening by mobile charge species from a bulk electrolyte, as well as a diverse set of electrochemical reactions at the solid-liquid interface. Understanding such complex processes requires techniques capable of mapping with a lateral resolution below the micron level. Traditional microscopic electrochemical methods based on current measurements in the time-domain or the frequency-domain do not allow measurements significantly below a fabricated device level, however. To date, scanning electrochemical microscopy (SECM)1 is the standard in measuring the local electrochemical behavior at solid-liquid interfaces. The spatial resolution of SECM requires the use of an ultra-micro electrode probe that limits the achievable resolution to micron scales, much larger than those achievable using standard scanning probe microscopy (SPM) techniques.
In ambient or vacuum environments, SPM techniques based on force detection can lead to a significant improvement over current based detection. For example, electrochemical strain microscopy (ESM) is capable of probing electrochemical reactivity and ionic flows in solids with nanometer resolution. Kelvin probe force microscopy (KPFM) is another example, widely used for the measurement of the surface potential distribution at gas-solid interface. Force based detection offers several major advantages over current detection based technologies: (a) the resolution to probe nanometer-scale volumes, (b) significantly improved sensitivity (i.e., enhanced signal to noise ratio), and (c) spectroscopy imaging capabilities. However, in order to gain an understanding of the local electrostatic, electrochemical, and double layer ion distribution, force based SPM techniques must be extended to the solid-liquid interface.
To date, KPFM is only operational under vacuum or ambient environments and in non-polar liquids. KPFM operation in polar liquids is complicated by the presence of mobile ions, preventing measurements under conditions relevant for biological or energy research, for example. The present application provides an SPM strategy to probe charge dynamics and electrokinetic phenomena in a technique referred to herein as electrochemical force microscopy. As discussed herein, electrochemical force microscopy can provide quantitative force-based electrochemical measurements of complex electrochemical reactions at the solid-liquid interface.